Such control valves are necessary for the regeneration of the absorption element through which volatile fuel passes during the normal operation of an internal combustion engine. The regeneration of the absorption element is achieved by passing fresh air therethrough. DE-PS 38 02 664 discloses such a control valve which consists of an electromagnetic valve and a pneumatic valve connected in series, controlled as a function of the intake suction pressure of the internal combustion engine.
This control valve has the disadvantage that an optimal regeneration of the absorption element cannot be obtained with optimal operating behavior of the internal combustion engine even for a substantially closed pneumatic valve, since the cyclically controlled electromagnetic valve is unsuitable for the extremely sensitive control of air flow due to too high an amplitude of the valve stroke and the effect of the mass of the biassing spring at the given frequency.
Additionally, the operation of the pneumatic valve is dependent on atmospheric pressure with respect to its control behavior, which makes it highly sensitive.